U.S. patent application number 10/145657 was filed with the patent office on 2003-11-06 for hierarchically ordered porous oxides.
Invention is credited to Chmelka, Bradley, Deng, Tao, Feng, Pingyun, Pine, David, Stucky, Galen, Whitesides, George M., Yang, Peidong, Zhao, Dongyaun.
Application Number | 20030205853 10/145657 |
Document ID | / |
Family ID | 26804252 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030205853 |
Kind Code |
A1 |
Yang, Peidong ; et
al. |
November 6, 2003 |
Hierarchically ordered porous oxides
Abstract
A low-cost, efficient method of preparing hierarchically ordered
structures by combining, concurrently or sequentially,
micromolding, latex templating, and cooperative self-assembly of
hydrolyzed inorganic species and amphiphilic block copolymers.
Inventors: |
Yang, Peidong; (Berkeley,
CA) ; Deng, Tao; (Somerville, MA) ;
Whitesides, George M.; (Newton, MA) ; Stucky,
Galen; (Goleta, CA) ; Zhao, Dongyaun;
(Shanghai, CN) ; Chmelka, Bradley; (Goleta,
CA) ; Pine, David; (Santa Barbara, CA) ; Feng,
Pingyun; (Goleta, CA) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI L.L.P.
Miles Yamanaka
Twenty-Ninth Floor
865 South Figueroa
Los Angeles
CA
90017-2571
US
|
Family ID: |
26804252 |
Appl. No.: |
10/145657 |
Filed: |
May 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10145657 |
May 14, 2002 |
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09432920 |
Nov 2, 1999 |
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6541539 |
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60106982 |
Nov 4, 1998 |
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Current U.S.
Class: |
264/603 ;
525/242; 528/480 |
Current CPC
Class: |
B82Y 30/00 20130101;
C04B 35/624 20130101; C04B 38/0051 20130101; C04B 2111/00405
20130101; C04B 35/622 20130101; C04B 38/0051 20130101; C04B 35/01
20130101; C04B 38/0045 20130101 |
Class at
Publication: |
264/603 ;
528/480; 525/242 |
International
Class: |
B28B 001/00 |
Goverment Interests
[0002] This invention was made with Government support under Grants
No. DMR-9520971 (GDS), DMR-9257064 (BFC), and DMR-9632716, awarded
by the National Science Foundation and Grant No. DAAH-04-96-1-0443
from the U.S. Army Research Office. The Government has certain
rights in this invention.
Claims
1. A method of forming a multi-scale mesoscopically structured
material, comprising: combining an amphiphilic block copolymer with
an inorganic metal compound; applying pressure to said combination,
whereby the block copolymer and inorganic metal compound are
self-assembled and polymerized into a mesoscopically structured
material; and polymerizing said mesoscopically structured
material.
2. The method of claim 1, wherein said amphiphilic block copolymer
and said inorganic metal compound combine to form a sol.
3. The method of claim 1, wherein pressure is applied to said
combination by placing said combination on a substrate, placing a
mold on said combination and applying said pressure to said
mold.
4. The method of claim 3, wherein said combination dewets said
substrate whereby to permit contact between said mold and said
substrate where no mesoscopically structured material is
desired.
5. The method of claim 3, further comprising after polymerizing the
mesoscopically structured material, of removing said mold to form a
mesoporous material.
6. The method of claim 1, further comprising after polymerizing the
mesoscopically structured material, calcining said material whereby
to remove said amphiphilic block copolymer thereby to form a
mesostructured material with a multiple length scale.
7. The method of claim 6, wherein said multiple length scale is
approximately 10 and 100 nm.
8. The method of claim 1, wherein said inorganic metal compound is
a transition metal compound.
9. The method of claim 1, wherein said inorganic metal compound is
a sulfide.
10. The method of claim 1, wherein said block copolymer is a
triblock copolymer.
11. The method of claim 10, wherein said triblock copolymer is a
poly(ethylene oxide)-poly(alkylene oxide)-poly (ethylene oxide)
polymer where the alkylene oxide moiety has at least three carbon
atoms.
12. The method of claim 10, wherein said triblock copolymer is
poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide).
13. The method of claim 1, wherein said mesoscopically structured
material has a cubic mesostructure.
14. The method of claim 1, wherein said mesoscopically structured
material has a hexagonal mesostructure.
15. The method of claim 1, wherein said metal compound, upon
calcination, forms an oxide selected from Nb.sub.2O.sub.5,
TiO.sub.2, ZrO.sub.2, WO.sub.3, AlSiO.sub.3,5, AlSiO.sub.5.5,
SiTiO.sub.4, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, SiO.sub.2,
SnO.sub.2, HfO.sub.2, ZrTiO.sub.4, and Al.sub.2TiO.sub.5.
16. The method of claim 1, wherein the pressure applied was about
1.times.10.sup.5 to 2.times.10.sup.5 Pa.
17. The method of claim 1, further comprising combining a latex
colloidal suspension with said combination, prior to applying
pressure to said combination, whereby to form a mesoscopically
structured material exhibiting multiple structural ordering length
scales of approximately 10, 100, and 1000 nm.
18. The method of claim 17, wherein said combination and said latex
colloidal suspension are combined at a volume ratio of 1:1.
19. The mesoscopically structured material of claim 1 having a
multiple structural ordering scale.
20. The mesoscopically structured material of claim 19 wherein the
multiple structural ordering length scale is approximately 10 and
100 nm.
21. A method of forming a multi-scale mesoscopically structured
material, comprising: contacting a mold, having a first open end
and a second open end, with a substrate; filling said mold with a
latex colloidal suspension; combining an amphiphilic block
copolymer with an inorganic metal compound; and filling said mold
with said combination whereby th e block copolymer and inorganic
metal compound are self-assembled and polymerized into a
mesoscopically structured material exhibiting multiple structural
ordering length scales.
22. The method of claim 21, wherein said structural ordering length
scales approximately 10, 100, and 1000 nm.
23. The method of claim 21, further comprising removing said mold
to form both a mesoporous and macroporous material.
24. The method of claim 21, wherein said block copolymer is a
triblock copolymer.
25. The method of claim 24, wherein said triblock copolymer is a
poly(ethylene oxide)-poly(alkylene oxide)-poly (ethylene oxide)
polymer where the alkylene oxide moiety has at least three carbon
atoms.
26. The method of claim 24, wherein said triblock copolymer is
poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide).
27. The method of claim 21, wherein said mesoscopically structured
material has a cubic mesostructure.
28. The method of claim 21, wherein said mesoscopically structured
material has a hexagonal mesostructure.
29. The method of claim 21, wherein said inorganic metal compound
is a transition metal compound.
30. The method of claim 21, wherein said inorganic metal compound
is a sulfide.
31. The method of claim 21, wherein said metal compound, upon
calcination, forms an oxide selected from Nb.sub.2O.sub.5,
TiO.sub.2, ZrO.sub.2, WO.sub.3, AlSiO.sub.3,5, AlSiO.sub.5.5,
SiTiO.sub.4, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, SiO.sub.2,
SnO.sub.2, HfO.sub.2, ZrTiO.sub.4, and Al.sub.2TiO.sub.5.
32. The method of claim 21, wherein said amphiphilic block
copolymer and said inorganic metal compound combine to form a
sol.
33. The method of claim 21, further comprising after filling said
mold, of polymerizing said mesoscopically structured material.
34. The method of claim 33, further comprising after polymerizing
the mesoscopically structured material, of removing said mold to
form a mesoporous material.
35. The method of claim 33, further comprising after polymerizing
the mesoscopically structured material, calcining said material
whereby to remove said amphiphilic block copolymer thereby to form
a mesostructured material with a multiple length scale.
36. The mesoscopically structured material of claim 21 having a
multiple structural ordering scale.
37. The mesoscopically structured material of claim 36 wherein the
multiple structural ordering length scale is approximately 10, 100,
and 1000 nm.
38. A method of forming a multi-scale mesoscopically structured
material, comprising: creating a sol in which an amphiphilic block
copolymer is combined with an inorganic precursor compound;
providing a substrate on which said sol is placed; providing a mold
on said sol and said substrate; applying pressure to said mold,
whereby to compress said sol between said substrate and said mold
and whereby the block copolymer and inorganic transition metal
compound are self-assembled and polymerized into a mesoscopically
structured material; and polymerizing said mesoscopically
structured material.
39. A method of forming a multi-scale mesoscopically structured
material, comprising: placing a mold, having a first open end and a
second open end, on a substrate; filling said mold with a latex
colloidal suspension, whereby to form an array thin the mold;
creating a sol in which an amphiphilic block copolymer is combined
with an inorganic precursor compound; and filling said mold with
said sol whereby the block copolymer and inorganic metal compound
are self-assembled and polymerized into a mesoscopically structured
material exhibiting multiple structural ordering length scales.
Description
CROSS-REFERENCE WITH RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/106,982, filed Nov. 4, 1998.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention relates to a method for synthesis of
hierarchically ordered materials at multiple length scales using
polyalkylene oxide triblock copolymers.
[0005] 2. Description of Related Art
[0006] Nature abounds in hierarchical structures that are formed
through highly coupled and often concurrent synthesis and assembly
process over both molecular and long-range length scales. [Aksay,
et al., Science, Vol. 273, 892 (1996)]. The existence of these
hierarchical structures, such as abalones and diatoms, has both
biological and evolutionary significance. The special architecture
of the natural structures make them simultaneously hard, strong,
and tough. It has thus been a long-sought goal to mimic the natural
process responsible for these exquisite architectures using
biomimetic strategies to control the structural organization and
thereby produce useful materials with similar architecture.
[0007] Several approaches are currently available for the
preparation of ordered structures at different length scales. For
example, organic molecular templates can be used to form zeolitic
structures with ordering lengths less than 3 nm [Bu, P., et al.,
Science, Vol. 278, 2080 (1997)]. Mesoporous materials with ordering
lengths of 3-30 nm can be obtained using surfactants or amphiphilic
block copolymers as the structure-directing agents [C. T. Kresge,
et al., Nature, Vol. 359, 710 (1992); D. Zhao, et al., Science,
Vol. 279, 548 (1998); P. Yang, et al., Nature, Vol. 399, 48 (1998);
A. Firouzi, et al., J.Am.Chem.Soc. Vol.119, 9466 (1997); and S. H.
Tolbert, et al., Science, Vol. 278, 264 (1997)].
[0008] Studies have shown the use of latex spheres affords
macroporous materials with ordering lengths of 100 nm-1 .mu.m [O.
D. Velev, et al., Nature, Vol. 389, 447 (1997); M. Antonietti, et
al., Adv. Mater., Vol. 10, 154 (1998); B. T. Holland, et al.,
Science, Vol. 281, 538 (1998); and J. E. G. J. Wijnhoven, et al.,
Science, Vol. 281, 802 (1998)]. Soft lithography has also been
shown to make high-quality patterns and structures with lateral
dimensions of about 30 nm to 500 .mu.m. [Y. Xia, et al., Angew.
Chem. Int. Ed., Vol. 37, 550 (1998); E. Kim, et al., Adv. Mater.
Vol. 8, 245 (1996); and C. Marzolin, et al., Adv. Mater. Vol. 10,
571 (1998)].
[0009] Previous studies have shown use of micromolding to form
patterned mesoporous materials [H. Yang, et al., Adv. Mater., Vol.
9, 811 (1997); and M. Trau, et al., Nature, Vol. 390, 674(1997)].
These studies, however, used acidic aqueous conditions to carry out
the cooperative self-assembly, which is disadvantageous because of
the poor processibility of the aqueous solutions. [Q. Huo, et al.,
Nature, Vol. 368, 317 (1994)]. The results of these studies were
that either non-continuous films were formed or an electric field
was needed to guide the mesophase growth, which required a
non-conducting substrate [H. Yang, et al., supra; and M. Trau, et
al., (1997), supra]. Studies have also shown the use of latex
spheres to make disordered macro- and mesoporous silica [M.
Antonietti, et al., supra].
[0010] Although previous studies addressed the synthesis of
disordered mesoporous silica and alumina, using nonionic
surfactants as the structure-directing agents and alkoxides as the
inorganic sources, under aqueous media, the studies did not address
large-pore mesoporous materials with vastly different composition,
and nanocrystalline frameworks [Sayari, A., Chem. Mater. Vol.
8,1840 (1996)].
[0011] Despite all of earlier efforts in nanostructuring materials,
the fabrication of hierarchically ordered structures at multiple
length scales has remained an experimental challenge. Such
materials are important both for systematic fundamental study of
structure-property relationships and for their technological
promise in applications such as catalysis, selective separations,
sensor arrays, waveguides, miniaturized electronic and magnetic
devices, and photonic crystals with tunable band gaps [D. Zhao, et
al., Adv. Mater. Vol. 10, 1380 (1998) and M. E. Gimon-Kinsel, et
al., Stud. Surf. Sci. Cata., Vol. 117, 111 (1998)].
[0012] Many applications for macro- and mesoporous metal oxides
require structural ordering at multiple length scales. Thus, there
exists a need for hierarchically ordered materials and a method for
forming the materials which overcome or minimize the above
mentioned problems and which have enormous potential for a variety
of immediate and future industrial applications. A need also exists
for forming the hierarchically ordered materials using low-cost,
non-toxic, and biodegradable polyalkylene oxide block
copolymers.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention overcomes drawbacks of the foregoing
methods to prepare mesoporous materials and mesoscopic structures
having orders at multiple length scales, and provides heretofore
unattainable materials having very desirable and widely useful
properties. These materials are prepared by combining amphiphilic
block copolymer with an inorganic metal compound, preferably by
creating a sol-gel solution. The amphiphilic block copolymer
species acts as a structure-directing agent for the inorganic metal
compound in self-assembling systems. Pressure is applied to the
combination, thus the block copolymer and inorganic metal compound
are self-assembled and polymerized into a mesoscopically structured
material.
[0014] In another embodiment of this invention, the combination,
preferably a sol, is placed on a substrate and a mold is placed on
top of the sol and the substrate. An effective amount of pressure
is applied to the mold and substrate, the amount of pressure is
preferably between about 1.times.10.sup.5 to 2.times.10.sup.5 Pa,
whereby the sol-gel solution is compressed between the substrate
and the mold. The mold is left in place, undisturbed, for at least
about 12 hours to allow increased cross-linking and consolidation
of the inorganic oxide network, thus the block copolymer and
inorganic metal compound are self-assembled and polymerized into a
mesoscopically structured material. The mold is then removed and
the resulting patterned material is calcined to yield the patterned
mesoscopically ordered porous material having a multiple length
scale. Calcination occurs at 300.degree. C. to 600.degree. C.,
preferably at about 400.degree. C.-450.degree. C. Unlike previous
mesoscopically ordered materials, the materials described in this
invention can be produced with multiple length scales on the order
of approximately 10 nm and 100 nm.
[0015] In accordance with a further embodiment of the invention
mesoporous materials and mesoscopic structures having orders at
multiple length scales are synthesized. Synthesis is carried out by
contacting a mold, which ends have been cut, with a substrate. A
mold is filled with a latex colloidal suspension, whereby an array
is formed within the mold. An amphiphilic block copolymer is then
combined with an inorganic metal compound, preferably by creating a
sol, and the mold is filled with the sol whereby the block
copolymer and inorganic metal compound are self-assembled and
polymerized into a mesoscopically structured material exhibiting
multiple structural ordering length scales on the order of
approximately 10, 100, and 1000 nm.
[0016] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following detailed description, appended claims, and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1a and 1b are schematic diagrams of the molding methods
used to fabricate hierarchically ordered structures on a substrate;
FIG. 1a is a schematic diagram for patterning of mesoporous solids,
a droplet of sol-gel/block copolymer precursor solution was
compressed between the silicone mold and the substrate by applying
pressure; FIG. 1b is a schematic diagram of a sequential process
for producing hierarchical ordering over three discrete and
independent length scales.
[0018] FIGS. 2a-2d are scanning electron microscope (SEM) images of
different patterns of mesoporous silica (FIGS. 2a-2c) and niobia
(FIG. 2d) formed using the scheme of FIG. 1a; materials shown in
(FIGS. 2a and 2c) are made of hexagonally ordered mesoporous silica
prepared using the amphiphilic block copolymer
E0.sub.20P0.sub.70E0.sub.20 (Pluronic P-123) as the structure
directing agent; the material shown in FIG. 2b is made of cubic
mesoporous silica prepared using the block copolymer
E0.sub.106PO.sub.70EO.sub.106 (Pluronic F-127); FIG. 2d shows a
hexagonally ordered mesoporous niobia prepared using Pluronic P-123
block copolymer.
[0019] FIG. 3 is a SEM image of a typical structure of
hierarchically ordered titania.
[0020] FIGS. 4a-4d are SEM images, at different magnifications, of
hierarchically ordered mesoporous silica possessing organization
over three discrete characteristic dimensions, prepared using the
scheme of FIG. 1b; FIGS. 4b and 4d show a diamond lattice of the
macroporous framework skeleton; FIGS. 4e and 4f are transmission
electron microscope (TEM) images of FIGS. 4a-4d, showing that the
framework of the macroporous skeleton is made up of ordered cubic
mesoporous silica with an ordering length of approximately 11 nm;
this sample was synthesized using Pluronic F-127 block copolymer as
the structure-directing agent.
[0021] FIGS. 5a and 5b are SEM images of hierarchically ordered
materials with three distinct order length scales, prepared using
the scheme of FIG. 1a, with isolated pattern features; FIG. 5c is a
TEM image of FIGS. 5a and 5b, confirming that the macroporous
framework of the material is made up of cubic mesoporous silica
similar to FIGS. 4a-4d.
[0022] FIG. 6 is a schematic diagram of the microtransfer molding
methods used to fabricate hierarchically ordered structures on a
substrate.
[0023] FIG. 7 is an optical microscope image of the microtransfer
molding method used to prepare mesoporous silica; the
inorganic/block copolymer solution was used as the liquid precursor
solution.
[0024] FIGS. 8a and 8b are SEM images of hierarchically ordered
materials with three distinct order length scales prepared using
the scheme of FIG. 6, with isolated pattern features; FIG. 8c is a
TEM image of FIGS. 8a and 8b, confirming that the macroporous
framework of the material is made up of cubic mesoporous silica
similar to FIGS. 4a-4d.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The present application is directed to an efficient
preparation of hierarchically ordered structures with
three-dimensional structures ordered over multiple length scales.
The ordered structures are prepared by combining concurrently or
sequentially the techniques of micromolding, latex templating, and
cooperative self-assembly of hydrolyzed inorganic species and
amphiphilic block copolymers. The resulting materials show
hierarchical ordering over several discrete and tunable length
scales ranging from about 10 nm to several micrometers. The
respective ordering structures can be independently modified by
choosing different mold patterns, latex spheres and block
copolymers.
[0026] The inorganic species includes: metal alkoxides; metal
chlorides; metal oxides; such as Nb.sub.2O.sub.5, TiO.sub.2,
ZrO.sub.2, WO.sub.3, AlSiO.sub.3,5, AlSiO.sub.5.5, SiTiO.sub.4,
Al.sub.2O.sub.3, Ta.sub.2O.sub.5, SiO.sub.2, SnO.sub.2, HfO.sub.2,
ZrTiO.sub.4, Al.sub.2TiO.sub.5, and sulfides. The metal alkoxides,
metal halides, and metal oxides can be transition metal alkoxides,
transition metal chlorides, and transition metal oxides. The
"transition metal", as used herein, is an element designated in the
Periodic Table as belonging to Group IIIB (e.g., scandium and
yttrium), Group IVB (eg., titanium, zirconium and hafnium), Group
VB (e.g. chromium, molybdenum and tungsten), Group VIIB (e.g.,
manganese, technitium and rhenium), Group VIIIB (iron, ruthenium,
osmium, cobalt, rhodium, iridium, nickel, palladium and platinum),
Group IB (e.g., copper, gold and silver) and Group IIB (zinc,
cadmium and mercury).
[0027] Commercially available, low-cost, non-toxic, and
biodegradable amphiphilic poly(alkylene oxide) block polymers can
be used as the structure-directing agents in non-aqueous solutions
for organizing the network forming metal compound species.
Preferably the block copolymer is a triblock copolymer in which a
hydrophilic poly(alkylene oxide) such as polyethylene oxide
(EO.sub.x) is linearly covalent with the opposite ends of a
hydrophobic poly(alkylene oxide) such as poly(propylene oxide)
(PO.sub.y) or a diblock polymer in which, for example,
poly(ethylene oxide) is linearly covalent with poly(butylene oxide)
(BO.sub.y). This can variously be designated as follows:
[0028] poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene
oxide)
[0029]
HO(CH.sub.2CH.sub.2O).sub.x(CH.sub.2CH(CH.sub.3)O).sub.y(CH.sub.2CH-
.sub.2O).sub.xH
[0030] EO.sub.xPO.sub.yEO.sub.x or
[0031] poly(ethylene oxide)-poly(butylene oxide)-poly(ethylene
oxide)
[0032]
HO(CH.sub.2CH.sub.2O).sub.x(CH.sub.2CH(CH.sub.3CH.sub.2)O).sub.yH
[0033] PEO-PBO-PEO
[0034] EO.sub.xBO.sub.yEO.sub.x
[0035] where x is 5 or greater and y is 30 or greater, with no
theoretical upper limit to either value subject to practical
considerations. Amphiphilic block copolymers with different
architectures, molecular weight or concentrations have been used to
obtain the third ordering structure that can be either hexagonal or
cubic with ordering length between about 5 nm to 20 nm.
[0036] The synthesis of the precursor solution was outlined in D.
Zhao, et al., Science, Vol. 279, 548 (1998) and Zhao, et al., Adv.
Mater, Vol.10, 1380 (1998). Tetraethoxysilane (TEOS),
tetramethoxysilane (TMOS), and tetrapropoxysilane (TPOS) were
suitable sources of silica for the preparation of mesoporous silica
structures. Hexagonal mesoporous silica structures were formed in
acid media (pH<1) with HCl, HBr, HI, HNO.sub.3, H.sub.2SO.sub.4,
or H.sub.3PO.sub.4 acids. In Zhao, et al., Adv. Mater, Vol.10,
oligomeric silica sol-gel was obtained by pre-hydrolyzing of TEOS
in ethanol by an acid catalyzed. The oligomeric silica sol-gel was
then added into a mixture solution of poly(ethylene
oxide)-poly(propylene oxide)-poly(ethylene oxide) PEO-PPO-PEO
triblock copolymers or alkyl poly(ethylene oxide) and inorganic
metal precursor compound in water and ethanol. The final
composition of this mixture was (in molar ratio) 0.0068-0.034
EO.sub.20PO.sub.70EO.sub.20 triblock copolymer :0.51 to about 3.0
inorganic metal compound: 1 tetraethylorthoxysilicane (TEOS):11-50
ethanol (EtOH): 0.002-0.04 HCl: 18-65 H.sub.2O.
[0037] In a typical synthesis, 2.08 g TEOS were added to 5 g
ethanol, 0.4 g water and 0.4 g (0.1 M) of HCl solution with
stirring at room temperature for 0.5 hours, then heated at
70.degree. C. without stirring for 1 hours. After cooling to room
temperature, 1 g EO.sub.20PO.sub.70EO.sub.20 (average molecular
weight 5800), 1 g NaCl, 10 g ethanol and 10 g water were added to
this solution with stirring at room temperature for 1 hour. The
samples are then calcined at about 400.degree. C. to 450.degree. C.
for about 5 hours to remove the block copolymer. For the Al and
SiAl metal oxides, calcination is carried out at 600.degree. C. for
4 hours. For WO.sub.3, calcination at 3000.degree. C. is sufficient
to yield ordered mesoporous oxides.
[0038] Table 1 summarizes the synthetic conditions, including the
inorganic precursors and aging temperatures and times for the
mesostructured inorganic/copolymer composites (before calcination)
using EO.sub.20PO.sub.70EO.sub.20 as the structure-directing agent.
The ordering lengths shown in Table 1 correspond to the largest d
value observed from low-angle XRD patterns; it ranged from about 70
to 160 .ANG. for the different systems.
[0039] In practicing this invention, one can use a commercially
available latex colloidal suspension containing latex spheres to
template the second level ordering structure. A latex suspension
containing polymer, preferably polystyrene, microspheres with sizes
ranging from about 50 nm to 1500 nm is preferred. The latex spheres
are also preferably uniform in size. The latex suspension used in
the following examples was obtained from Bangs Laboratory, Fishers,
Ind.
[0040] The substrate used in the following examples was a freshly
cleaned silicon wafer, however, other substrates such as glass,
quartz, and polymers may be substituted for the silicon wafer.
Besides ethanol, other organic solvents, such as methanol,
1,4-dioxane, tetrahydrofuran (THF), CH.sub.3CN, and propanol, can
be used as solvents. The mold used in the following examples was a
poly(dimethylsiloxane) (PDMS) mold. The procedure for making the
mold is outlined in Y. Xia, et al., Angew. Chem. Int. Ed. 37, 550
(1998). The patterned structures of the resulting materials can
have a thickness of a submicron to several tens micrometers
depending on the relief depth of the micromold used. One skilled in
the art may practice the invention using any mold having micro
features.
[0041] Mesoscopic ordering in the synthesized materials was
characterized by their low-angle X-ray diffraction patterns and
transmission electron microscope (TEM) images. All TEM images were
recorded on a JEOL 2010 transmission electron microscope operated
at 200 KeV. The scanning electron microscope (SEM) images were
taken on a JEOL F6300 scanning electron microscope operated at 3
KeV.
[0042] During latex templating, it is believed that the
organization of latex spheres in confined geometries involves
nucleation due to capillary attractive forces between the
microspheres and growth due to evaporation and influx of suspension
to compensate for the loss of solvent. [See, E. Kim, et al., Adv.
Mater. Vol. 8, 245 (1996)]. The different packing sequences
observed in the larger triangular and the smaller bridge areas are
presumably the consequence of the different edge effects during the
colloidal organization. [See, A. van Blaaderen, et al., Nature,
Vol. 385, 321 (1997)]. In addition, the inorganic oxide, e.g.,
silica, framework of the macroporous structure is itself made up of
mesoscopically ordered cubic arrays of cages with characteristic
dimension of approximately 11 nm as established by the Pluronic
F-127 block copolymer. FIGS. 4e and 4f show typical TEM images
recorded for the same hierarchically ordered silica. The ordered
macroporous structure (approximately 100 nm) can be seen in FIGS.
4a-4f, along with the silica framework consisting of ordered cubic
arrays of mesopores (approximately 11 nm).
[0043] The formation of end-caps in self-assembled surfactant
cylinders is not favored given their high free energy of formation.
Thus, within the highly confined geometries of the PDMS micromold,
the cylindrical block copolymer aggregates are expected to oriented
preferentially parallel to the micromold walls in order to minimize
the number of aggregate end-caps. These patterned lines of
mesoporous silica can be potentially used as waveguides. In
addition, combining these patterning capabilities and the high
porosities achievable, greater than 70%, for such mesoporous silica
is extremely promising for low-dielectric material applications
related to the miniaturization of electronic circuits and
devices.
[0044] Many applications of macro- and mesoporous metal oxides
require structural ordering at multiple length scales. Development
of such strategies for hierarchically ordered materials using
low-cost, non-toxic, and biodegradable polyalkylene oxide block
copolymers has enormous potential for a variety of immediate and
future industrial applications. A continuing challenge for
materials chemists and engineers is the ability to create
multifunctional composite structures with well-defined superimposed
structural order from nanometer to micrometer length scales
[0045] Many uses have been proposed for patterned Macro- and
mesoporous metal oxide materials, particularly in the fields of
catalysis, molecular separations, fuel cells, adsorbents,
optoelectronic devices, and chemical and biological sensors. For
example, the patterned lines that were demonstrated for mesoporous
silica and other metal oxides can be potentially used as
waveguides. In addition, the combination of the patterning
capabilities and the high porosities achievable for such mesoporous
materials is extremely promising for dielectric material
applications related to the miniaturization of electronic circuits
and devices. [D. Zhao, et al., Adv. Mater., Vol. 10, 1380 (1998)].
Macro- and mesoporous Nb.sub.2O.sub.5 can be potentially used as an
ultra-sensitive humidity sensor. [M. E. Gimon-Kinsel, et al., Stud.
Surf. Sci. Cata., Vol. 117, 111 (1998)].
[0046] The resulting materials showed hierarchical ordering over
several discrete and tunable length scales ranging from 10 nm to
several micrometers. The respective ordering structures can be
independently modified by choosing different mold patterns, latex
spheres and block copolymers. The versatility of this invention is
exemplified by the syntheses of patterned macro- and mesoporous
materials of various compositions, such as silica, niobia, and
titania, which have various physical properties including
semiconducting, low dielectric-constant, and high dielectric
constants.
[0047] The hierarchical ordering process can be further extended to
the preparation of other patterned mesoporous metal oxides, such as
TiO.sub.2 using sol-gel mesophase self-assembly chemistry developed
in our laboratory. Particularly interesting for hierarchically
ordered TiO.sub.2 is the possibility of fabricating photonic
crystals with tunable photonic band gap in the visible and infrared
region. Other possible applications include optical filter and
antenna. There is also tremendous interest in using mesoporous
ZrO.sub.2, AlSiO.sub.3,5, AlSiO.sub.5.5, and SiTiO.sub.4 as acidic
catalysts. Mesoporous materials with semiconducting frameworks,
such as WO.sub.3 and SnO.sub.2 can also be used in the construction
of fuel cells.
[0048] Thus, such materials are important both for systematic
fundamental study of structure-property relationships and for their
technological promise in applications such as catalysis, selective
separations, sensor arrays, waveguides, miniaturized electronic and
magnetic devices, and photonic crystals with tunable band gaps.
EXAMPLE 1
[0049] FIG. 1a illustrates the procedure that was used to fabricate
materials with two scale ordering. Here, the gelation of a
self-assembling sol-gel precursor solution was carried out in the
confined space of a poly(dimethylsiloxane) (PDMS) mold, the
procedure for which is outlined in Y. Xia, et al., Angew. Chem.
Int. Ed., Vol. 37, 550 (1998), incorporated herein by
reference.
[0050] The precursor solution had the same composition as used in
the preparation of mesoporous silica films outlined in D. Zhao, et
al., Science, Vol. 279, 548(1998) and Zhao, et al., Adv. Mater,
Vol.10, 1380 (1998).
[0051] The sol-gel precursor solution of the present invention
consisted of 0.008-0.018
poly(ethyleneoxide)-b-poly(propyleneoxide)-b-poly(ethylene- oxide)
(EO.sub.nPO.sub.mEO.sub.n) triblock copolymer: 1
tetraethylorthoxysilicane (TEOS):20-60 ethanol (EtOH): 0.01-0.04
HCl: 5-10 H.sub.2O. Pluronic P-123 (EO.sub.20PO.sub.70EO.sub.20)
was used as the triblock copolymer.
[0052] To mold these materials, a drop of the precursor solution
was put on a freshly cleaned substrate (e. g. silicon wafer) after
which the mold was placed face down to cover the drop on the
surface of the substrate. A pressure of roughly 1.times.10.sup.5 to
2.times.10.sup.5 Pa was applied to the PDMS mold. The area of the
patterned surface was typically 1-5 cm.sup.2 with molded feature
sizes in the micrometer size range. It is important that the liquid
dewets the surface to permit contact between the PDMS elastomer and
the substrate in regions where no mesostructured material is
desired. This dewetting is driven by both the applied pressure and
the difference between the interfacial tensions of the precursor
and the PDMS mold. [See, C. Marzolin, et al., Adv. Mater. Vol. 10,
571 (1998)]. Gelation of the mesophase precursor solutions normally
occurred within hours. The mold and the resulting mesostructure
were left undisturbed for at least 12 h to allow increased
cross-linking and consolidation of the inorganic oxide network.
After removing the mold, the patterned material was calcined at
400.degree. C. in air for 5 h to remove the amphiphilic block
copolymer species and thereby produce patterned mesoscopically
ordered porous solids.
RESULTS OF EXAMPLE 1
[0053] Mesoscopic ordering in these materials is characterized by
their low-angle X-ray diffraction patterns and transmission
electron microscope (TEM) images. FIGS. 2a and 2c show several
representative scanning electron microscope (SEM) images of the
dual-scale synthesized ordered materials. The structural ordering
observed at the micrometer level was imparted by the micromolding
operation using the PDMS mold, while the mesoscopic ordering
results from the self-assembly of the sol-gel block copolymer
solution. Both isolated (FIG. 2a) and continuous (FIG. 2b) features
can be produced by this overall process. The materials shown in
FIGS. 2a and 2c are hexagonal mesoporous silica (cell parameter
a=approximately 10.5 nm). The smallest line feature obtained with
the micromolding was about 100 nm (FIG. 2c).
EXAMPLE 2
[0054] The procedure of Example 1 was followed, substituting
Pluronic F-127 (EO.sub.106PO.sub.70EO.sub.106) for Pluronic P-123
(EO.sub.20PO.sub.70EO.sub.20) as the structure-directing triblock
copolymer species.
RESULTS OF EXAMPLE 2
[0055] The results of using Pluronic F-127
(EO.sub.106PO.sub.70EO.sub.106) as the triblock copolymer was the
material synthesized was cubic mesoporous silica (cell parameter
a=approximately 11 nm), as seen in FIG. 2b.
EXAMPLE 3
[0056] The procedure of Example 1 was followed by substituting
NbCl.sub.5 as the inorganic metal precursor compound. 1 g of
Pluronic P-123 (EO.sub.20PO.sub.70EO.sub.20) was dissolved in 10 g
of ethanol. To this solution, 0.01 mole of NbCl.sub.5 was added
with vigorous stirring.
RESULTS OF EXAMPLE 3
[0057] FIG. 2d shows a representative SEM image of a dual-scale
synthesized ordered Nb.sub.2O.sub.5 material, which is a potential
ultra-sensitive humidity sensor.
EXAMPLE 4
[0058] The procedure of Example 1 was followed by substituting
TiCl.sub.4 as the inorganic metal precursor compound. 1 g of
Pluronic P-123 (EO.sub.20PO.sub.70EO.sub.20) was dissolved in 10 g
of ethanol. To this solution, 0.01 mole of TiCl.sub.4 was added
with vigorous stirring.
RESULTS OF EXAMPLE 4
[0059] FIG. 3 shows a SEM image of a typical structure of
hierarchically ordered titania.
EXAMPLE 5
[0060] To obtain materials with ordering on three discrete length
scales, latex templating was combined sequentially or concurrently
with micromolding and cooperative self-assembly. The sequential
process is illustrated in FIG. 1b. Both ends of the PDMS mold were
cut open to allow fluid to enter and air/solvent to escape. The
mold was then placed on a freshly cleaned Si substrate. The
compliant nature of the PDMS elastomer allowed conformal contact
between the mold and the substrate, and a network of channels
formed. A drop of a latex colloidal suspension containing
polystyrene microspheres (200 nm diameter, 10 weight % in water)
was placed at one cut end of the PDMS mold, so that the fluid
suspension filled the network of the micromold channels by
capillary action.
[0061] Upon evaporation of the solvent at room temperature, the
latex spheres organized into a close-packed array within the
confinement of the micromold channel network. A drop of sol-gel
block copolymer precursor solution, containing the same composition
as in Example 1, was subsequently placed at the same end of the
mold and similarly imbibed into the latex-sphere filled micromold
channels by capillary action. The PDMS mold and contents were then
left undisturbed for at least 12 hours, during which time
cross-linking and polymerization of the inorganic oxide precursor
species occurred to yield a robust composite product. The mold was
removed and the resulting materials were calcined at 450.degree. C.
in air for 2 hours to remove the block copolymer species and the
polystyrene spheres.
RESULTS OF EXAMPLE 5
[0062] The synthesized materials exhibited hierarchical ordering
with discrete characteristic length scales of 10, 100, and 1000 nm
in a single body. FIGS. 4a-4d illustrate several typical SEM images
for these ordered structures. The structural organization over the
three independent length scales was achieved by combining block
copolymer self-assembly, latex-sphere templating, and micromolding
to produce ordered mesopores (10 nm), macropores (100 nm), and
surface patterns (1000 nm). Micromolding resulted in high quality
surface patterns with micron size dimensions (FIG. 4a); the
patterned features themselves were made of the inorganic oxide
solid organized to form highly ordered macropores that had been
templated by close-packed arrays of the latex spheres (FIGS.
4b-4d). The high degree of macropore ordering (approximately 100
nm) was clearly observed both in the triangular features seen in
FIG. 4b and within the bridges observed in FIG. 4c, although FIGS.
4b and 4c show different packing sequences.
EXAMPLE 6
[0063] In order to fabricate materials with three hierarchically
ordering length scales into isolated patterned structures, the
procedure of Example 1 was followed, with the addition of combining
a latex sphere suspension with the sol-gel/triblock copolymer in a
volume ration of 1:1. In this example, a drop of sol-gel/block
copolymer and latex sphere suspension (volume ratio 1:1) was placed
on the substrate before application of the PDMS mold.
RESULTS OF EXAMPLE 6
[0064] FIGS. 5a and 5b show SEM images of such isolated surface
pattern features with ordering lengths of both approximately 1000
and 100 nm, which resulted from micromolding and latex-sphere
templating, respectively. The TEM image (FIG. 5c) and low angle
X-ray diffraction patterns of these materials further confirmed
that the inorganic oxide (silica) frameworks of the macropore
structures consisted of highly ordered mesopore arrays.
EXAMPLE 7
[0065] The technique of microtransfer molding was used to prepare
materials with two scale or three scale ordered porous material. In
this microtransfer molding process a drop of liquid inorganic
precursor solution was applied to the patterned surface of a PDMS
mold and the excess liquid was removed by scraping with a flat PDMS
block. The liquid precursor used was the inorganic/block copolymer
solution. The filled mold was then placed in contact with a silicon
wafer substrate. A pressure of about 1.times.10.sup.5 to
2.times.10.sup.5 Pa was then applied to the mold and the
mold/substrate structure was left undisturbed for at least 12
hours, to ensure the proper cross-linking of the inorganic
frameworks. The mold was peeled away carefully to leave a patterned
structure on the surface of the substrate. This structure was then
calcined at 450.degree. C. to remove the block copolymer and the
latex spheres.
RESULTS OF EXAMPLE 7
[0066] FIG. 7 shows an optical microscope image of the mesoporous
silica fabricated by microtransfer molding.
EXAMPLE 8
[0067] The procedure of Example 7 was followed, by substituting a
mixture of latex suspension and inorganic/copolymer solution (in a
volume ratio of 1:1) for the inorganic/block copolymer liquid
precursor solution.
RESULTS OF EXAMPLE 8
[0068] FIGS. 8a and 8b show SEM images of typical structures of
hierarchically ordered silica that were fabricated by microtransfer
molding. FIG. 8c shows a TEM image of FIGS. 8a and 8b. The TEM
image and low angle X-ray diffraction patterns of these materials
further confirmed that the inorganic oxide frameworks of the
macropore structures consisted of highly ordered mesopore arrays.
This method was also capable of generating both isolated and
interconnected microstructures. However, residual materials cannot
usually be avoided between the patterned raised features.
EXAMPLE 9
[0069] The procedure of EXAMPLE 7 was followed by substituting the
step of removing the excess liquid precursor solution by blowing
off with a stream of nitrogen or air for the removal by scraping
with a flat PDMS block.
EXAMPLES 10 to 21
[0070] The procedure of Example 1 can be followed, by preparing a
sol-gel solution as disclosed in P. Yang, et al., Science, Vol.
282, 2244 (1998), incorporated by reference herein, with diverse
thermally stable mesostructured metal oxides, including ZrO.sub.2,
WO.sub.3, AlSiO.sub.3,5, AlSiO.sub.5.5, SiTiO.sub.4,
Al.sub.2O.sub.3, Ta.sub.2O.sub.5, SiO.sub.2, SnO.sub.2, HfO.sub.2,
ZrTiO.sub.4, Al.sub.2TiO.sub.5, and sulfides. The metal oxides may
be used in the sol-gel solution by slowing hydrolysis of inorganic
chloride precursor species in alcohol solutions. Table 1 summarizes
the synthetic conditions for the mesostructured inorganic/copolymer
composites.
[0071] The syntheses of these hierarchically ordered materials
demonstrate the ability to control the overall structure of the
inorganic materials at several discrete and independent ordering
length scales. It is the self-assembly of sol-gel inorganic/block
copolymer mesophase around organized arrays of latex spheres in a
patterned mold that leads to structures with such high
complexities. The respective ordering lengths and structures can be
independently modified by choosing a different mold pattern, latex
spheres with different diameters, and/or amphiphilic block
copolymers with different architectures, molecular weight or
concentrations. Furthermore, the composition of the inorganic
framework can be altered by using appropriate sol-gel inorganic
precursor species, e.g, Nb.sub.2O.sub.5, TiO.sub.2, ZrO.sub.2,
WO.sub.3, AlSiO.sub.3,5, AlSiO.sub.5.5, SiTiO.sub.4,
Al.sub.2O.sub.3, Ta.sub.2O.sub.5, SiO.sub.2, SnO.sub.2, HfO.sub.2,
ZrTiO.sub.4, Al.sub.2TiO.sub.5, and even sulfides. [See, P. Yang,
et al., Nature, Vol. 396, 152 (1998)].
[0072] These materials possess both biomimetic significance and
technological importance. The ease, reproducibility, and
versatility of this synthetic approach facilitates the development
of new materials with a variety of compositions, and offers
far-ranging possibilities for tuning electronic, optical, and
magnetic properties over several length scales independently. For
example, hierarchically ordered titania may exhibit tunable
photonic band gaps. Foreseeable technological applications of these
materials include quantum optics or optical communications, large
molecular catalysis, separation, host-guest systems, porous
electrodes, and sensors.
[0073] The following references are incorporated herein by
reference: A. Aksay, et al., Science, 273, 892 (1996); X. Bu, et
al., Science, 278, 2080 (1997); C. T. Kresge, et al., Nature, 359,
710 (1992); D. Zhao, et al., Science, 279, 548 (1998); P. Yang, et
al., Science, Vol. 282, 2244 (1998); P. Yang, et al., Nature, Vol.
396,152 (1998); A. Firouzi, et al., J. Am.Chem. Soc. 119, 9466
(1997); S. H. Tolbert, et al., Science, 278, 264 (1997); D. Velev,
et al., Nature, 389, 447 (1997); M. Antonietti, et al., Adv. Mater.
10, 154 (1998); B. T. Holland, et al., Science, 281, 538 (1998); J.
E. G. J. Wijnhoven, et al., Science, 281, 802 (1998); Y. Xia, et
al., Angew. Chem. Int. Ed. 37, 550 (1998); E. Kim, et al., Adv.
Mater. 8, 245 (1996); C. Marzolin, et al., Adv.Mater. 10, 571
(1998); H. Yang, etal., Adv. Mater. 9, 811 (1997); M. Trau, et al.,
Nature, 390, 674 (1997); Q. Huo, et al., Nature, 368, 317 (1994);
D. Zhao, et al., Adv. Mater., Vol.10, 1380 (1998); S. L. Keller, et
al., Phys. Rev. Lett. 80, 2725 (1998); Q. Huo, et al., Adv. Mater.
9, 974 (1997); M. E. Gimon-Kinsel, et al., Stud. Surf. Sci. Cata.
117, 111 (1998); and A. van Blaaderen, et al., Nature, 385, 321
(1997).
[0074] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
and understanding, it will be obvious that various modifications
and changes which are within the knowledge of those skilled in the
art are considered to fall within the scope of the appended
claims.
1TABLE 1 Aging Aging System Inorganic Precursor Temperature,
.degree. C. time (day) d (.ANG.) Zr ZrC1.sub.4 40 1 125 Ti
TiC1.sub.4 40 7 123 Al AlC1.sub.3 40 2 130 Si SiC1.sub.4 40 2 171
Sn SnC1.sub.4 40 2 124 Nb NbC1.sub.5 40 2 106 Ta TaC1.sub.5 40 2
110 W WC1.sub.6 60 15 126 Hf HfC1.sub.4 40 1 124 Ge GeC1.sub.4 40
15 146 V VC1.sub.4 60 7 111 Zn ZnC1.sub.2 60 30 120 Cd CdC1.sub.2
40 7 111 In InC1.sub.3 60 30 124 Sb SbC1.sub.5 60 30 93 Mo
MoC1.sub.5 60 7 100 Re ReC1.sub.5 60 7 121 Ru RuC1.sub.3 40 3 95 Ni
NiC1.sub.2 40 2 100 Fe FeC1.sub.3 40 7 116 Cr CrC1.sub.3 40 4 117
Mn MnC1.sub.2 40 7 124 Cu CuC1.sub.2 40 7 98 SiAl
AlC1.sub.3/SiC1.sub.4 40 2 120 Si.sub.2Al AlC1.sub.3/SiC1.sub.4 40
2 120 ZrTi ZrC1.sub.4/TiC1.sub.4 40 2 110 Al.sub.2Ti
AlC1.sub.3/TiC1.sub.4 40 7 112 SiTi SiC1.sub.4/TiC1.sub.4 40 3 103
ZrW.sub.2 ZrC1.sub.4/WC1.sub.6 40 3 140 SnIn SnC1.sub.4/InC1.sub.3
40 30 83
* * * * *